The present invention relates to a drill specifically designed for drilling cavities or apertures in bones during the performance of surgical procedures.
In performing surgical procedures involving the repair of bones, the setting of broken bones or the replacement of joints, it is frequently necessary to drill cavities or apertures suitable for receiving bone screws. For example, in the case of fractures, the screws may be utilized for securing bone plates for fixation of the fractured sections. Screws may also be used in a variety of joint replacements and compression hip plates among other applications.
Prior art drills for use in bone surgery are difficult to precisely position during the drilling process. The prior art drills are derivative of metal cutting drills and have a tendency, at the beginning of the drilling operation, to move slightly from the desired axis of the aperture being drilled. This difficulty is particularly pronounced when the surgeon is attempting to start the drilling process on a portion of the bone which has a non-flat surface. Prior art bone drills have points which are not self-retaining on the desired axis. This is particularly true for drills for forming apertures having a diameter greater than about 1/841 .
Additionally, the prior art bone drills have tips which do not immediately start the cutting operation when the tip contacts the bone surface. In order to overcome the problem with respect to accurate positioning of the prior art drills, the surgeons were forced to either (1) using a bushing to guide the drill, (2) use a relatively smaller drill as a starter and use the desired diameter drill in a subsequent operation or (3) attempt to start the drilling at a flat part of the bone, at an oblique angle to the desired axis of the cavity or aperture, and then straighten the drill to the desired axis. None of these solutions is particularly satisfactory and frequently result in the cavity or aperture being drilled having an irregular, non-cylindrical surface. This can lead to premature loosening of the screws. The prior art drills, when used with drill guides, result in excessive wear between the drill and drill guide causing wear debris to be generated which can lead to bone necrosis or infection which could lead to loosening of the screws. The other prior art procedures using prior art bone drills can also result in excessive bone debris being generated which can rapidly fill the flutes leading to generation of excessive heat and more bone necrosis.
Under the present invention, there is provided a drill which can be used in a one-step drilling operation with precise positioning and immediate retention along the desired axis upon contact of the tip with the bone. The drill of the present invention has a stabilizing point having tapered cutting edges with adjacent flutes. The tapered cutting edges extend to the tip and begin the cutting action immediately upon contact of the stabilizing point with the bone. Spaced axially from the tip of the stabilizing point are spaced apart cutting edges lying on a plane perpendicular to the axis of the drill which are arcuately displaced from one another approximately 180.degree.. These spaced apart cutting edges follow a straight line path and, after the start, cooperate with the stabilizing point (a) to prevent the drill from "walking" or moving off the desired axis, (b) to assure that the cavity being cut is round or cylindrical even if the aperture is being cut at an oblique angle on a circular surface and (c) to prevent packing of bone chips by causing the chips to be readily expelled from the site being drilled. The drill of the present invention permits the drilling of an aperture or cavity in the bone in a one-step operation even though the origin of the drilling is a non-flat bone surface. It has a fluted design which permits bone chips to be augured away from the bone interface with the result that less heat is transferred to the bone interface than with prior art drills thus lessening bone necrosis.
The present invention is also directed to a method for forming an aperture or cavity in a bone.